Study On Pore Structure And Surface Functional Groups Of Polyaniline-based Activated Carbon To Improve The Performance Of Supercapacitors

Supercapacitors have attracted much attention because of their excellent cycling performance and super high power density.Activated carbon is the most widely used electrode material in commercial supercapacitors.In this paper,the pore structure and the effect of surface functional groups on electrochemical properties of activatedcarbon are studied.Mainly includes the following four parts.?1?Activated carbon?AC?is the electrode material used most for supercapacitors,which is of low cost and wide source.The physical activation method of co-activation with water vapor-carbon dioxide?H₂O?gas?-CO₂?to prepare AC is widely applied in the large-scale production of commercial activated carbon.The activation products prepared with this method are of no activator residue,easy cleaning,environmental friendly and so on.In the present work,polyaniline is used as raw material to explore the effect of the amount of H₂O?gas?and CO₂ partial pressure on the activated product.AC surface area and pore volume reach 2357 m²·g^-11 and 1.45 cm³·g^-1,respectively.This sample serves as an electrode material for ionic liquid?EMIMBF₄?capacitors with a high capacitance up to 203 F·g^-11 and excellent rate performance as well as good cycle stability with 91%capacitance retention after 10000 cycles(5 A·g^-1).?2?The low temperature performance of supercapacitors with ionic liquid is extremely poor due to the increase of ion transport resistance at low temperature.Therefore,it is especially important to study the charge/discharge mechanism of supercapacitors with organic electrolyte at low temperature.In the present work,it is found that the presence of a large number of submicropores?0.7-2 nm?in AC would greatly improve the low temperature performance of supercapacitors at-40°c.Compared with 25°C,the capacitance retention of-40°C can reach 90%.It is proposed that a new desolvation mechanism with combination of experimental results and theoretical calculation.Electrolyte ions with solvents tend to be gradually desolvented in submicropores.Meanwhile,it is discovered that the functionalized activated carbon?FCNSs?combined with sub-micropore and mesopore structure has a high specific capacitance of up to 131 F·g^-1,and the capacitance retention can reach about 100%at-40°C.?3?Among the various hybrid capacitors with various metals as negative electrodes,zinc-ion hybrid capacitor is the most promising energy storage devices except lithium-ion hybrid capacitors.A new type of zinc-ion hybrid capacitor with functionalized activated carbon as positive electrode and zinc as negative electrode is invented to reveal the microscopic mechanism of proton transfer effect in ionic liquid and organic electrolyte.It has been found that the proton transfer effect can greatly improve the comprehensive electrochemical performance of hybrid capacitors.The energy density?2.4V?of the devices made is as high as 54.3 Wh·L^-11 in ionic electrolyte.While in organic electrolyte,the energy density of the device is 18.8Wh·L^-1,and the power density of the device is as high as 17.7 kW·L^-1,charge and discharge only take 11 seconds.More importantly,stable cycles is up to 60000 cycles and capacitance retention is up to 100%at a high current density of 10 A·g^-1.?4?Another type of capacitor is made with AC containing hydrogen functional groups?FACs?prepared by one-step activation as positive electrode,zinc as negative electrode and ZnSO₄ aqueous solution as electrolyte.It is found that the comprehensive electrochemical performance of activated carbon materials containing hydrogen functional groups?-OH and-NH functional groups?could be improved by controlling the microporous structure.FACs sample has a capacitance of 435 F·g^-1and excellent cycling stability,capacitance retention up to 89%after charging and discharging cycles 10000 at 2 A·g^-1.It is found that the proton transfer effect is more obvious on capacity when the PH value is low,the capacitance is up to 544 F·g^-11 at PH=3.DFT calculations also prove the mechanism of proton transfer effect in aqueous electrolyte.